Tumor metastasis is thought to depend on cell adhesion between blood-borne tumor cells, circulating platelets (facilitating platelet-tumor emboli), and endothelia, promoting arrest in the vasculature, growth, and extravasation. Tang et al., Invasion Metastasis, 14: 109-122, 1994; McEver et al., Glycoconjugate J., 14: 585-591, 1997; Krause et al., Clin. Exp. Metastasis, 17: 183-192, 1999. Several types of adhesion receptors and ligands have been described as important elements in this process, including selecting, chemokines and integrins. Tang et al., Invasion Metastasis, 14: 109-122, 1994; Kannagi, Glycoconjugate J., 14: 577-584, 1997; Behrens, Breast Cancer Res. Treat., 24: 175-184., 1993. Overall, these features of tumor cell adhesion resemble characteristics of leukocyte extravasation during inflammation. In both cases, expression of the oligosaccharides, sialyl Lewis X [sLeXSiaα2,3Galβ1, 4(Fucα1,3)GlcNAc] and sialyl Lewis a[sLeaSiaα2,3Galβ1,3(Fucα1,4)GlcNAc] on cell-surface glycoconjugates endows cells with the ability to adhere to E-, P-, and L-selectins present on endothelia, platelets, or leukocytes. Studies of human tumors and mice bearing genetic alterations in one or more selectins underscore the importance of these interactions in hematogenous spread of cancer cells. Biancone et al., J. Exp. Med., 183: 581-587, 1996; Renkonen et al., Int. J. Cancer, 74: 296-300, 1997; Frenette et al., Thromb Haemost, 78: 60-64, 1997; Kim et al., Proc. Natl. Acad. Sci. USA, 95: 9325-9330, 1998; Borsig et al., Proc. Natl. Acad. Sci. USA, 98: 3352-3357, 2001.
The carbohydrate ligands for the selectins are predominantly O-linked glycoprotein mucins and glycolipids that display sLeX or sLea in clustered arrangements. Fukuda, Cancer Res., 56: 2237-2244, 1996; Kansas, Blood, 88: 3259-3287, 1996; Kim et al., Am. J. Pathol., 155: 461-472, 1999. Several aggressive solid tumors display significant reactivity to anti-sLeX monoclonal antibodies and E- and P-selectins. These include a relatively large proportion of tumors from the lung, colon, and breast. Kannagi, Glycoconjugate J., 14: 577-584, 1997; Renkonen et al., Int. J. Cancer, 74: 296-300, 1997; Kim et al., Am. J. Pathol., 155: 461-472, 1999; Fukushima et al., Cancer Res., 44: 5279-5285, 1984; Kannagi et al., Cancer Res., 46: 2619-2626, 1986; Mannori et al., Cancer Res., 55: 4425-4431, 1995; Nakamori et al., J. Clin. Oncol., 15: 816-825, 1997. Adhesion interactions involving sLeX constitute important early steps in the pathophysiology of metastasis possibly by stabilizing “neoplastic emboli” via P-selectins on platelets or L-selectin on leukocytes, or by facilitating adhesion to and possible extravasation thorough the endothelium. Kim et al., Proc. Natl. Acad. Sci. USA, 95: 9325-9330, 1998; Borsig et al., Proc. Natl. Acad. Sci. USA, 98: 3352-3357, 2001; Rice et al., Science, 246: 1303-1306, 1989; Stone et al., J. Clin. Invest., 92: 804-813, 1993; Honn et al., Cancer Metastasis Rev., 11: 325-351, 1992; Frenette et al., J. Exp. Med., 191: 1413-1422, 2000. The importance of these interactions derives from studies in patients post-resection from colon, lung, gastric, and other carcinomas that show that survival correlates inversely with tumor expression of sLeX. Ogawa et al., J. Thorac. Cardiovasc. Surg., 108: 329-336, 1994; Nakamori et al., Dis. Colon Rectum, 40: 420-431, 1997; Baldus et al., Tumour Biol., 19: 445-453, 1998.
Research has focused on the development of small molecule inhibitors that might block the expression of Lewis carbohydrate antigens on cells. Per-O-acetylated disaccharides (acetylated forms of Galβ1,4GlcNAcβ-O-naphthalenemethanol [AcGGn-NM] or GlcNAcβ1,3Galβ-O-naphthalenemethanol [AcGnG-NM]) are taken up by cells, deacetylated, and acted on as substrates by relevant glycosyltransferases located in the Golgi. Assembly of oligosaccharides on the disaccharides takes place, resulting in diversion of glycan biosynthesis from endogenous glycoconjugates. Sarkar et al., Proc. Natl. Acad. Sci. USA, 92: 3323-3327, 1995; Sarkar et al., J. Biol. Chem., 272: 25608-25616, 1997; Sarkar et al., Carbohydr. Res., 329: 287-300, 2000. The result is a concomitant reduction of sLeX expression on the cell surface. The monosaccharide, GalNAcα-O-benzyl, behaves in a similar fashion, altering the expression of O-linked chains on mucins of colon and leukemia cell lines in vitro and altering cell adhesion to platelets and endothelia Niv et al., Int. J. Cancer, 50: 147-152, 1992; Kojima et al., Biochem. Biophys. Res. Commun., 182: 1288-1295, 1992; Delannoy et al., Glycoconjugate J., 13: 717-726, 1996. However, much higher concentrations of the monosaccharide are needed to achieve a similar level of inhibition as the disaccharide (1-5 mM versus 10-50 μM, respectively). Fuster et al., Cancer Research 63: 2775-2781, 2003; Sarkar et al., Proc. Natl. Acad. Sci. 92: 3323-3327, 1994; Hindsgaul et al., J. Biol. Chem. 266:17858-17862, 1991; Khan et al., J. Biol. Chem. 268: 2468-2473, 1993; Lowary et al., Carbohydr. Res. 251:33-67, 1994; Linker et al., Carbohydr. Res. 245: 323-331, 1993. A need exists in the art for more potent inhibitors that block the expression of Lewis carbohydrate antigens on cells and can act as a therapeutic agent to control or prevent tumor metastasis.